1. Field of the Invention
The present invention relates to dispense valves and, more particularly, to precision dispense valves for controllably dispensing minute increments of a fluid in metered amounts at selectable rates.
2. Description of the Problem and Prior Art
Valves for dispensing selected quantities of fluid, either liquid or gas, are used in a great variety of applications. For example, a large variety of valves are used in the medical field. In addition, valves of various types are used in the field of nutrition, automatic food and beverage dispensing and processing, analysis machines such as wet chemistry analysis machines and water quality analysis machines, titration equipment, manufacturing in general, gas metering, fuel oil metering, and so on. Dispensing valves are also used as atomizing valves.
One common requirement of most of the valves used today is that they operate automatically in response to a stimulus, such as an electrical signal. Many of the valves presently available are quite adequate for their intended application. However, where a high degree of accuracy is required to dispense a precise volume of material automatically, available valves fall short. More particularly, where applications require a precise volume to be dispensed over a given period of time under, for example, computer control, existing valves are deficient. Such applications not only require the mechanical valve arrangement to operate accurately and reliably, they also require the valve control function to accurately respond to variations in electrical signal with the precision of the dispensing operation being at least a partial function of how closely the signals represent the true requirements of the system. It has been found that valves which operate in an on/off or binary mode to dispense fluid, as opposed to varying the orifice size, are more advantageous in metering applications.
Typical of prior art dispensing valves is that described by Lombard et al in U.S. Pat. No. 3,795,383. Lombard et al show a ball-type solenoid valve for dispensing fluid. Although the Lombard et al valve is a binary-type valve, i.e. on/off-type, it lacks process control capability such as to function to meter fluid in accordance with the frequency or repetition rate of the applied control signal. Accordingly, the Lombard et al valve is not capable of the accuracy and precision required by many applications and this is due in part, at least to the fact that the valve ball is held in place against the fluid pressure by an electromagnet and fluid is dispensed in response to de-energizing the magnet.
Another prior art ball-type valve arrangement is that described by Loe in U.S. Pat. No. 3,731,670. The Loe valve is designed as a binary or on/off valve for use within a duct of an animal body and, as such, employs an extracorporeal means to operate the valve. Loe uses an external magnet to manually move the magnetically sensitive ball from its closed seat position to an open position.
U.S. Pat. No. 3,355,145 to de Castelet also discloses a ball-type valve arrangement held in its closed position by an electromagnet, akin to the Lombard et al valve described above. Like Lombard et al, de Castelet operates in an on/off mode such that when the electromagnet is energized the ball is held in its seat to block fluid flow and when the electromagnet is de-energized, fluid forces the ball away from its seat to permit fluid to be dispensed.
Another valve arrangement typifying the prior art is the arrangement described by Brous in U.S. Pat. No. 2,609,974. Brous describes a volumetric dispensing valve for vending machines and the like using a solenoid driven magnetized pellet operative to empty fluid contained in the valve body. The Brous valve lacks close precision and accuracy and this is due, in part at least, to the fact that it cannot respond to control signals that take into account fluid temperature, viscosity and flow characteristics.